Development of a swirling jet in infinite space

We examine the problem of swirling-jet development in an infinite space filled with the same fluid. The fourth term of the asymptotic expansion of the tangential-velocity component is obtained. The constant appearing in the solution is obtained semlempirically. Results are presented of calculations of the velocities and pressure in swirling jets and of experimental studies.Swirling jet flows play an important role in the process of combustion intensification and stabilization and are widely used in engineering.The formulation and first solution of the problem of swirling-jet development in an infinite space filled with the same fluid at rest were accomplished by Loitsyanskii [1], who found the first two terms of the asymptotic expansion of the solution of the boundary-layer equations. The third and fourth terms of the asymptotic expansion of the axial-velocity component were found in [2], which made it possible to study the effect of jet swirl on the axial-velocity-component profile.In the present study we obtain the fourth term of the asymptotic expansion of the tangential-velocity component and present results of experimental studies on swirling jets.The authors wish to thank L. G. Loitsyanskii for valuable comments.     

Numerical modeling of a two-dimensional vertical turbulent two-phase jet

The results of numerically modeling two-dimensional two-phase flow of the “gas-solid particles” type in a vertical turbulent jet are presented for three cases of its configuration, namely, descending, ascending, and without account of gravity. Both flow phases are modeled on the basis of the Navier-Stokes equations averaged within the framework of the Reynolds approximation and closed by an extended k-? turbulence model. The averaged two-phase flow parameters (particle and gas velocities, particle concentration, turbulent kinetic energy, and its dissipation) are described using the model of mutually-penetrating continua. The model developed allows for both the direct effect of turbulence on the motion of disperse-phase particles and the inverse effect of the particles on turbulence leading to either an increase or a decrease in the turbulent kinetic energy of the gas. The model takes account for gravity, viscous drag, and the Saffman lift. The system of equations is solved using a difference method. The calculated results are in good agreement with the corresponding experimental data which confirms the effect of solid particles on the mean and turbulent characteristics of gas jets.     

An experimental study of a two-dimensional plane turbulent wall jet

 Laser-Doppler measurements were conducted in a plane turbulent wall jet at a Reynolds number based on inlet velocity, Re ₀, of 9600. The initial development as well as the fully developed flow was studied. Special attention was given to the near-wall region, including the use of small measuring volumes and the application of specific near-wall data corrections, so that wall shear stresses were determined directly from the mean velocity gradient at the wall using only data below y ⁺=4. It was possible to resolve the inner peak in the streamwise turbulence intensity as well as the inner (negative) peak in the shear stress. Limiting values of (u′)⁺ and uv ⁺ were determined. Turbulence data from the outer region of the flow were compared to earlier hot wire measurements and large differences in the normal turbulence intensity and the shear stress were found. These differences can be attributed to high turbulence intensity effects on the hot-wires. Received: 17 October 1996 / Accepted: 8 December 1997     

Types of wave structure in the interaction of a convergent jet with an infinite two-dimensional obstruction

Possible types of wave structure formed in the first roll of a convergent supersonic jet as it interacts with an infinite two-dimensional object are indicated in this work based on a generalization of results from theoretical and experimental studies. The influence of the Mach number, over pressure parameter n, isentropic exponent k, and the location h of the obstacle on the wave structure is considered.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 45–50, January–February, 1976.     

Propagation of an underexpanded turbulent jet in a parallel supersonic flow

The characteristics of supersonic off-design turbulent jets discharging into parallel supersonic flows are investigated numerically using approximate equations for the effective turbulent viscosity which are derived by analysis of the experimental data.     

Transient behavior of an axisymmetric turbulent jet

The prediction of the response of unsteady flows submitted to external excitation is a real challenge for the optimization of industrial processes. As the jet flow is a very basic turbulent flow related to mixing and entrainment phenomena via turbulent structure dynamic, we investigate the transient behavior of an axisymmetric jet submitted to a large and sudden decrease of its ejection velocity. The non stationary flow evolution is studied experimentally. Measurements along the jet axis based on pure ensemble averaging show clearly the convective motion of the perturbation and the adaptation of the local interaction to the local jet time scale. A transverse investigation in the non stationary region show that the mean flow and its turbulence is deeply affected during the local velocity decrease.     

Concentration fluctuations in a turbulent jet

Using Spalding's model of turbulence in a turbulent shear flow, we have calculated the root-mean-square value of the concentration fluctuations inside a turbulent jet. Although we used the same equations and the same solution technique as Spalding, we have not been able to find precisely his numerical results derived for a jet issuing into a fluid at rest with the same density as the jet. The differences between our numerical results, Spalding's numerical results and the experimental data of Becker, Hottel and Williams are fairly small only if the initial values of the turbulence energy and the mixing length inside the jet and the turbulence in the ambient fluid are taken into account in the model. For a turbulent jet issuing into a turbulently flowing surrounding stream of different density, we found that the relative concentration fluctuations can increase considerably. This brings out the importance of taking into account property variables in analysing turbulent mixing processes.     

Large eddy simulation in a turbulent jet exhausting into a submerged space or a cocurrent flow

Results of large eddy simulations in a subsonic isothermal turbulent jet exhausting from a circular nozzle into a submerged space or a cocurrent flow are presented. The flow is described by space-averaged Navier-Stokes equations and by the RNG model of subgrid scale viscosity. Results computed for different values of the cocurrency parameter are compared with available results of numerical simulations and experimental data. The results obtained are found to agree well with measured data and to confirm the basic laws of variation of gas-dynamic and fluctuating parameters of submerged and cocurrent jets.     

Hardy space infinite elements for time-harmonic two-dimensional elastic waveguide problems

We consider time-harmonic linear elasticity equations in domains containing two-dimensional semi-infinite strips. Since for such problems there exist modes with different signs of group and phase velocity, standard perfectly matched layer (PML) as well as standard Hardy space infinite element methods fail.We apply a recently developed infinite element method for a physically correct discretization of such waveguide problems which is based on a Laplace transform in propagation direction. In the Laplace domain the space of transformed solutions can be separated into a sum of a space of incoming and a space of outgoing functions where both function spaces are certain Hardy spaces. The Hardy space is chosen such that the construction of a simple infinite element is possible.The method does not use a modal separation and works on domains of frequencies. On those domains the involved operators are frequency independent and hence lead to linear eigenvalue problems when computing resonances. Numerical experiments containing convergence tests and resonance problems are included.     

Corona in a turbulent jet with condensation

The electrogasdynamic (EHD) effects associated with the introduction of corona discharge ions into a vapor-air jet with condensation are investigated. The electrical, acoustic and, moreover, integral and local optical (light scattered by condensate droplets) characteristics of the jet are measured. The time-dependent components of the recorded signals, which provide information about the characteristic fluctuations in the flow, are determined and processed. A new effect — the existence of a correlation between the electrical (Trichel frequency), acoustic and optical fluctuations in the flow — is detected and analyzed.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 28–35, July–August, 1992.     

Drop evaporation in a turbulent gas jet

Evaporation of a semidispersive drop system in a turbulent gas jet is considered. A method for calculating drop evaporation in a turbulent gas jet is proposed based on a simplified solution of the scattering problem for an evaporating admixture. Evaporation of water as it is atomized in a turbulent air jet is experimentally studied. Approximate agreement is obtained between the results of the calculations and experiments.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 73–79, January–February 1976.     

Velocity measurements in a two-phase turbulent jet

The motion of oil droplets in a round turbulent air jet is investigated experimentally. Direct information on the droplets' average velocity is obtained by means of a Laser Doppler velocimeter. Average velocity profiles of the droplets are measured along the axis of the jet and transverse to it. The results are compared to the free jet expansion.The jet Reynolds number is in the range 10⁴–10⁵, the droplets' diameters are 50 μm and below and the volume concentration of the oil in the air is 10^?6.At the jet exit, the air velocity is higher than the droplets' velocity, at the developed region of the jet the droplets' velocity is found to be higher than the free air jet velocity at the same location. In the radial direction, the velocity profiles of the droplets are self similar and the droplets' velocity is lower than the free air jet velocity at the same location. The droplets' velocity decay along the axis of the jet is slower than the air velocity in the free jet and the two-phase jet is narrower than the submerged free air jet at the same exit velocity.     

Round turbulent jet in a crossf low

We examine the discharge of a turbulent jet from a round opening into an infinite uniform crossflow and find the form of the jet centerline and the distribution of the maximum velocities in the jet along the axis. It is shown that the calculated jet axes and velocity distributions agree well with the experimental values for different ratios of the velocity at the source exit to the crossflow velocity and for different angles of entry of the jet into the crossflow. The study [1] formed the basis for the proposed semiempirical theory.     

Velocity gradients in a turbulent jet flow

We present a selection of results from experiments on an air turbulent jet flow, which included measurements of all the three velocity components and their nine gradients with the emphasis on the properties of invariant quantities related to velocity gradients (enstrophy, dissipation, enstrophy generation, etc.). This has been achieved by a 21 hot wire probe (5 arrays x 4 wires and a cold wire), appropriate calibration unit and a 3-D calibration procedure [1]. A more detailed account on the results will be published elsewhere.     

Phase-averaged measurements in an isosceles triangular turbulent free jet

Digital time series hot-wire data, acquired in the near field of a turbulent free jet of air issuing from a sharp-edged isosceles triangular orifice, have been post-processed using a phase-averaging procedure to determine the coherent and random contributions to turbulence statistics. The Reynolds number, based on the equivalent diameter of the orifice, was 1.84×10⁵. It was found that momentum transfer by the Reynolds primary shear stress occurs mainly via the coherent primary shear stress.